The present invention relates to a seal means for an internal combustion engine such as a rotary piston engine which are provided at the interfaces of housings defining an engine working chamber and having formed therein passages constituting a circuit for flow of fluid coolant, and each of which is mounted in a groove means provided between the working chamber and coolant flow passages in at least one mating surface of a housing at an interface.
A rotary piston engine employs am epicyclically driven three-lobe rotor rotating in a chamber which is defined by a main engine casing including a main rotor housing having two open sides and having a generally trochoidal inner peripheral surface constituting a chamber wall contactable by the lobes of the rotor, and two side housings fixedly attached to opposite sides of and enclosing the open sides of the main housing, and which is divided by the rotor into three gas-tight compartments, the volume of each of which is varied as the rotor rotates, an explosive mixture supplied into the chamber via an intake port being compressed as the rotor rotates, and then ignited by a spark plug to produce an explosion providing force to continue rotation of the rotor, and exhaust gases being driven by the rotor to an exhaust port leading out of the chamber, during which time another intake of explosive mixture is supplied into the chamber. A commonly employed method for removal of heat resulting from the combustion processes taking place within the chamber is to circulate a fluid coolant in passages which are formed in the actual bodies of the main housing and side housings, passages formed in opposite side housings being in communication with passages formed in the main housing. Although side housings are fixedly attached to and are initially mounted in comparatively flush fit to the main housing, after the engine has been in service for a certain time there is inevitably some displacement of the side housings relative to the main housing, and thee are also produced narrow gaps between mating surfaces of the main housing and side housings, particularly since it is the practice to make the main housing and side housings of dissimilar metals, which may provide different electrode potentials promotive of electrochemical corrosion, and which have different temperature-expansion coefficients and therefore tend to move in frictional contact with one another in response to temperature variations accompanying successive cycles of engine operation, corrosion of housing surfaces at gaps formed being further encouraged by the electrolytic action of coolant infiltrating therebetween. Since the coolant flow passages formed in the main housing or a side housing open onto the mating surface thereof, to prevent coolant which is circulated in these passages from passing through a gap between mating surfaces and leaking into the working chamber of the engine, it is the practice to provide at each interface, i.e., where each pair of mating surfaces meet, seal means located between coolant passages and the working chamber and generally constituted by a ring which surrounds the periphery of the working chamber and is fitted into a groove formed in the mating surface of either the main housing or the side housing, and has dimensions such that it projects slightly from the groove when it is seated therein, whereby when the main and side housings are in an assembled condition the seal means is pressed firmly against the opposite mating surface. Qualities required of such a ring include of course good heat and corrosion resistance, and also, in order to ensure that the ring presses against the opposite mating surface in good sealing contact, the ring is required to have a certain degree of flexibility, and is therefore suitably made of an elastomeric material. However, since the ring is flexible, due to the effects of vibration and other motion when the engine is in operation, face and side corner portions of the ring may easily work into gaps formed at the housing interfaces, where they are subject to rapid deterioration and wear, thus permitting further ring portions to work into the gaps and resulting in failure of the seal means. To counter this phenomenon it has been known to provide the seal ring with a backup layer or element constituted by a thin metallic strip, which is annular in form and is provided in the seating groove and in contact with the outer side of the seal ring, i.e., the side thereof which is outermost with respect to the working chamber and closer to the coolant flow passages of the housing in which the seating groove is formed. By the nature of metallic products, this backup strip, as well as being strong is comparatively rigid, and it is not possible even initially to ensure a completely flush fit between the backup element and the opposite mating surface, even if the dimensions of the backup element are such that the element is pressed firmly against the opposite mating surface when the housings are assembled, in addition to which the backup element being of a comparatively thin cross section is particularly sensitive to the effects of corrosion or abrasion, with the result that there is always, or there is rapidly formed a gap between the backup element face and the mating surface of the opposite housing. Under the influence of even comparatively minor vibrations the main seal member of elastomeric material is liable to work into this gap, and in the extreme case is able to advance as far as the gap between housing mating surfaces and is subject to deterioration resulting in failure, as described before. Alternatively it has been known to provide the backup element in the form of a ring of strong but comparatively flexible material such as polytetrafluoroethylene. Such a backup element is able to be pressed firmly against a mating surface so as to leave no gap into which corner portions of the main member may work due to minor vibrations of the engine. However, when there occur vibratory or other forces able to cause a comparatively great deflection of the main member, the backup element, also being non-rigid, bends together with the main member and permits main member corner portions to move into a gap at an interface, again leading to failure of the seal means. To render a backup element made of polytetrafluoroethylene or similar material more rigid, it has been proposed to make the backup element thicker. But since housings must accommodate coolant flow passages, constitute a rigid outer casing defining the working chamber, and at the same time not be excessively bulky or heavy, there are constructional limitations on the permitted size of the groove for accommodation of the seal means, and increasing the thickness of the backup element therefore necessitates decreasing that of the main seal member, which consequently fails to function satisfactorily as a seal means.